AION effects Isotope Overdrive/Preamp - no output

[airvian]

Hello there!
I have run into an issue. My build has no output when switched on. For some reason I lose all the signal after the second OP-amp of the TL072 (IC1). I do get signal at pins 1, 2 and 3 but none at 6 or 7. I do however get signal at pins 2 of the bass and treble knobs as well as the adjacent caps and resistors (R6, C4). Anyone have an idea? I tried a different dual OP-amp but that didn't change a thing...

[duck_arse]

as with every build, we can't help without a layout diagram, a circuit diagram, some voltage measures.

[scum]

Are you confident about your soldering?many joints (solder joints)  seem a little suspect

[idy]

R6 and C4 re attached to pin 6 of the opamp. Are you saying you have signal on one side of both but not the other? That implies a short on that node where. the three things meet. Power off check for short (or low R) to ground.

[airvian]

as with every build, we can't help without a layout diagram, a circuit diagram, some voltage measures.

oh shoot I forgot to attach the schematic. The rest of the build documentation can be found here: https://aionfx.com/app/files/docs/isotope_documentation.pdf
The schematic is attached to the post.
Would the voltages on pins 5 through 8 of the TL072 help you?

[airvian]

Are you confident about your soldering?many joints (solder joints)  seem a little suspect

Yes. Solder joints have usually not been a problem for me (bar some exception where a joint cracked or didn't make proper connection on off-borad components). I did check every single one with a magnifying glass and, as a precaution, reheated and applied additional solder to the ones that seemed like they did not cover a soldering pad completely.

[airvian]

R6 and C4 re attached to pin 6 of the opamp. Are you saying you have signal on one side of both but not the other? That implies a short on that node where. the three things meet. Power off check for short (or low R) to ground.

So, I rechecked everything and found that there is no short on R6 or C4. I cranked my audio probe to the max setting and found that I actually do get a signal, it is just very faint. It drops to around 50% of original at pin 2 and 3 of IC1 (TL072) and never fully recovers.

[idy]

voltages?

and the question:
You are saying there is good signal on one end of C6 and R4?
And that signal is much weaker on the other side, the side attached to pin 6 of IC1?
And when, with power off, you checked for short or low resistance to ground from that node you found what? No connection at all?

Your solder joints do "look" OK, but one detail is watch how close you cut leads off after soldering: you don't want to slice into the solder so much.

Voltages? All opamp pins. Transistors too, but not important yet...

[airvian]

as with every build, we can't help without a layout diagram, a circuit diagram, some voltage measures.

Some voltages (in V) all to ground:
DC (from 9V battery): 9.65V

IC1 (TL072):
pin 1: 0.637
pin 2: 0.637
pin 3: 0.247
pin 4: 0.705
pin 5: 0 (is connected to ground)
pin 6: 0.064
pin 7: 0.777
pin 8: 9.40

IC2 (RC4558)
pin 1: 8.65
pin 2: 0.141
pin 3: 0 (connected to ground)
pin 4: 0.705
pin 5: 0.086
pin 6: 8.70
pin 7: 8.70
pin 8: 9.39

IC3 (TC1044)
pin 1: 9.39
pin 2: 7.59
pin 3: 5.050
pin 4: 3.258
pin 5: 0.706
pin 6: 6.32
pin 7: 7.58
pin 8: 9.38

Q1:
C: 9.44
B: 0
E: 0.719

Q2:
C: 9.43
B: 0
E: 0.719

Q3:
C: 0.719
B: 1.275
E: 0.712

[idy]

So the 1044 is not doing anything. It needs to put out about -9v on pin 5. Opamps will do nothing until that is fixed.

double check everything around 1044. Polarity of caps...

[airvian]

So the 1044 is not doing anything. It needs to put out about -9v on pin 5. Opamps will do nothing until that is fixed.

double check everything around 1044. Polarity of caps...

All values and polarities are correct.

[idy]

1044 is a problem.
Pin 3 should be grounded, 0v. Why isn't it?

You may have to turn power off and check for continuity, pin 3 to ground.

[ElectricDruid]

So the 1044 is not doing anything. It needs to put out about -9v on pin 5. Opamps will do nothing until that is fixed.

double check everything around 1044. Polarity of caps...

All values and polarities are correct.

Time to triple check then!!

IDY is right - there *must* be something wrong around that 1044 since the voltages aren't right. Could the -VA supply be shorted somewhere further from the chip, maybe?

Some of your solder joints look under-heated to me. I can tell because on one side there are blobs of solder like little footballs, but on the other side, almost no solder is visible on some joints. This is pretty common. Most people are told that you can kill components if you overheat them, so they tend to touch the solder for as little time as possible. But if you hold the iron on for just a second or two more, you'll see the through-hole plating get hot enough and the solder will "suck" into the hole. When that happens, you know that's enough.

HTH

[airvian]

voltages?

and the question:
You are saying there is good signal on one end of C6 and R4?
And that signal is much weaker on the other side, the side attached to pin 6 of IC1?
And when, with power off, you checked for short or low resistance to ground from that node you found what? No connection at all?

Your solder joints do "look" OK, but one detail is watch how close you cut leads off after soldering: you don't want to slice into the solder so much.

Voltages? All opamp pins. Transistors too, but not important yet...

Thank you for the tip regarding the solder joints. I will keep it in mind for all future soldering.
With power off the resistance from pin6 of IC1 is >2MOhm to outside the range. A connection from C4 and R6 to pin6 of IC1 is there.
Yes, the signal at pin 2 and 3 of IC1 is about 50% of the original and at pin 6 of IC1 it is significantly lower to almost undetectable if I don't crank the audio probe.

[idy]

OK so we are sure there is a problem around the 1044. Nothing will work until that is fixed. Nothing.
I don't think that first buffer is even working.

Why
no
ground
on
1044
pin 3?

no continuity to ground?
Why?

[airvian]

1044 is a problem.
Pin 3 should be grounded, 0v. Why isn't it?

You may have to turn power off and check for continuity, pin 3 to ground.

Problem solved. You reminding me of Pin 3 having to be grounded solved the issue. The PCB has SEVERAL soldering pads for ground. Usually when a PCB has that many grounds I omit most. I just don't like having that many ground connections. Turns out, not all ground connections on this PCB are created equal. While the IC in question was grounded to the GND connection next to the output pad that goes from the PCB to the footswitch, but not "global" ground. So I ran a wire from that pad to the GND on the footswitch as well and now it works. So now I have two grounds from the PCB to the footswitch, one each for the jacks and one for the LED as well as DC jack.... I have no idea why that is but that was the issue... If anyone knows why please explain, I'd be curious.

[ElectricDruid]

Lordy, they're right! There's three different grounds on that schematic! GND, PWR_GND and BYP_GND.

Noise is the most likely reason. I've separated Digital and Analog Ground on schematics a few times. Here I think they've done it to avoid high frequency noise from the charge pump getting into the ground circuit used by the audio path. Of course (as you've discovered) they have to be connected *somewhere*, but you generally want to give noisy bits of circuit their own ground path back to the supply.

If you connect different grounds on the schematic, the PCB software assumes they're all the same thing and it makes it much harder to layout a PCB with the ground divided into different areas. So the only way to do that is to *avoid* connecting them on the schematic and then connect them in reality.

Sorry, I hope that makes sense. It'd be easier to explain with some diagrams!

[idy]

 hallelujah.

[airvian]

Lordy, they're right! There's three different grounds on that schematic! GND, PWR_GND and BYP_GND.

Noise is the most likely reason. I've separated Digital and Analog Ground on schematics a few times. Here I think they've done it to avoid high frequency noise from the charge pump getting into the ground circuit used by the audio path. Of course (as you've discovered) they have to be connected *somewhere*, but you generally want to give noisy bits of circuit their own ground path back to the supply.

If you connect different grounds on the schematic, the PCB software assumes they're all the same thing and it makes it much harder to layout a PCB with the ground divided into different areas. So the only way to do that is to *avoid* connecting them on the schematic and then connect them in reality.

Sorry, I hope that makes sense. It'd be easier to explain with some diagrams!

Thanks. Yeah, makes total sense. I've never paid attention to this before - I will now. Doing this for noise seems logical as well. I've previously done builds that had a charge pump  but only had one ground. Usually I solved any such issues by swapping in and out some ICs and listening which model doesn't have the high pitch hum.

Anyhow: If anyone is interested in building this pedal it sounds really good. It's not really that unique sound wise but it really has some nice drive tones in it especially when hit with a boost (I use a bluesebreaker type circuit for that usually). The baxendall tome circuit they integrated into the design really gives it a very useful range from more creamy tones to really hairy higher gain tones (for my standards).